The present disclosure relates to a gas turbine engine and, more particularly, to a nozzle system therefor.
Gas turbine engines, such as those which power modern military aircraft, include a compressor section to pressurize a supply of air, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases and generate thrust. Downstream of the turbine section, an augmentor section, or “afterburner”, is operable to selectively increase thrust. The increase in thrust is produced when fuel is injected into the core gases downstream of the turbine section and burned with the oxygen contained therein to generate a second combustion that is then passed through a variable area nozzle system.
A variable area nozzle such as a convergent/divergent (C/D) nozzle optimizes the thrust produced within the gas turbine engine by provision of a multitude of nozzle positions. The term “convergent-divergent” describes a nozzle having a convergent section upstream of a divergent section. Gases from the turbine section pass through the decreasing diameter convergent section before passing through the increasing diameter divergent section. Convergent/Divergent (C/D) nozzles may be configured for an augmented or an un-augmented engine in a two or three-dimensional configuration with, or without, the capability to vector.
The nozzle defines a throat area and an exit area. The throat area is the minimum cross sectional area of the nozzle and is defined by the interface between an aft portion of the convergent section and a forward portion of the divergent section. The exit area is the cross sectional area measured at the aft most portion of the divergent section. The area ratio of a nozzle is the exit area divided by the throat area. The area ratio range provides a general indicator of engine performance and an increase in the area ratio range results in more efficient engine performance with increased engine thrust, fuel efficiency and a decrease in actuator loads required to articulate the nozzle as the engine power setting increases.
The convergent and divergent sections each generally include circumferentially disposed flaps and flap seals. The alternately disposed flaps and flap seals accommodate changes in jet area and nozzle axis skew (if the nozzle is vectorable). Support for such changes in area and nozzle axis skew requires a lightweight yet rigid interface between the nozzle section and the upstream attachment thereof.